1. Field of the Invention
The present invention relates generally to a drive unit for propelling a wheeled vehicle by frictional engagement of a power driven friction roller with one of the wheels of the vehicle, and more particularly relates to an improved drive unit provided with a multi-ratio speed transmission.
1. State of the Prior Art
Various systems and drive units of the friction type are known for use with wheeled vehicles, particularly with cycles.
Typically, the known drive units are auxiliary power drives or assists which comprise a drive motor and a friction roller coupled to the motor and supported in frictional engagement with the front or steerable wheel of the cycle. Rotation of the friction roller is transmitted by friction to the driven cycle wheel.
Exemplary of such known devices are the drives disclosed by Palmer in U.S. Pat. No. 4,113,043, Bialek in U.S. Pat. No. 3,841,428, Pennebaker, et al., in U.S. Pat. No. 4,221,275, and Kalajzich in U.S. Pat. No. 4,175,629.
All of these drives are characterized by the use of a battery powered electrical drive motor which has an output shaft which is either directly coupled to the friction roller, or is coupled to the friction roller by means of a belt drive as in Pennebaker, et al.
None of the friction drives of the type exemplified in the referenced patents or otherwise known to the applicant provide means for varying the speed ratio between the friction roller and the drive motor output shaft in a ready manner by an operator of the vehicle for optimum transmission of power to the friction roller under varying road and/or vehicle load conditions.
For example, it is desirable to provide a low gear ratio between the drive motor output shaft and the friction roller during starting of the vehicle, and during uphill climbing, in order to most effectively utilize the torque output of the motor and make best use of the limited battery power available. Such a low gear ratio, however, is not optimum for cruising on level stretches, and for this purpose a higher gear ratio is desirable. For intermediate conditions, at least one intermediate gear ratio is indicated.
Such a variable gear ratio device should be light weight, so as not to materially increase the load to be propelled, given the limited charge available from the batteries, should be economical since this type of drive is intended for low cost vehicles and it would defeat its purpose to substantially increase the cost of the drive, and, finally, should be simple to operate and reliable in its functioning since such power assist drives are frequently employed by the elderly or the handicapped.
A continuing need exists for a friction drive for cycle vehicles which meets the aforementioned criteria.